Asphaltenes are one of the most important components of the petroleum heavy crude oil that control its rheology due to their polarity, complexity of their amorphous structures, solubility in aromatic solvent, precipitation into n-alkane and their molecular weight variations. Their chemical structure and elemental composition depend on their origin, source rocks, and thermal history [1]. Their polarity is attributed to presence of heteroatoms included nitrogen, oxygen and sulfur and traces of metals, such as nickel, vanadium and iron. Asphaltenes produced as one of the bitumen (asphalt) components and may aggregate and precipitate during the downstream and upstream processes in the pipelines or storage tanks to cause many serious problems in production, refining and transportation. The chemical structure of asphaltenes are modified through substitution reactions on the polycondensed aromatic rings, and heterocyclic [2-4]. Moreover, the long alkyl chains, functional groups such as COOH, OH, NH, SH, etc., and conjugated dienes represent other functional groups on the asphaltene molecules can be also modified in a substitution, elimination, or addition reactions [2-4].
To minimize the harmful effects of asphaltenes it is important to better understand their structural characteristics that assist in increasing their interaction with resin to form big micelles and lower interaction with resin to form aggregates which are still a matter of dispute. The asphaltenes precipitation and aggregation were affected by variation of temperature and pressure of the reservoir [5]. The chemical inhibitors are more favored than thermal and mechanical methods to stabilize and disperse the asphaltenes to keep them suspended by stabilization mechanisms [6]. Recently, protic ionic liquids (PILs) as green solvents having low melting point, non-flammability, and higher thermal stability were used as asphaltene dispersants and for asphaltene solvent extraction from asphalt and coal [7-10].
The chemical structures of asphaltenes have been modified to produce valuable crude oil added materials via modification with sulfuric acid [11], blending with flow improver polymers to modify the rheology of crude oil [12], solubilizing in the hydrocarbon mixtures [13], blending with asphaltene dispersant polymers [14]. The asphaltenes were mixed to produce polymer composites [15] and also modified to produce surfactants through reacting with anhydride or halides [16]. Sulfonated asphaltenes were used to prepare hydrophobic magnetite to act as petroleum crude oil collector by an external magnetic field [17].
There is a need in the art for agents that prevent or reduce asphaltene aggregation and/or precipitation in order to prevent or lessen the problems that otherwise occur during production, storage, transportation and/or refining of a petroleum hydrocarbon fluid.